No-rinse phosphating process

ABSTRACT

A process for phosphating metal surfaces by treatment with an acidic zinc- and phosphathe-containing solution which does not require rinsing. The metal substrate is contacted with a phosphating solution containing 2 to 25 g/l of zinc ions, 2 to 25 g/l of manganese ions and 50 to 300 g/l of phosphate ions. The solution has a pH value of 1 to 3.6, a free acid content of 0 to 100 points, a total acid content of 40 to 400 points and a ratio of free acid to total acid of 1:4 to 1:20.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a phosphating solution and to a process forphosphating surfaces of steel, zinc, aluminium or their alloys. It isparticularly suitable for phosphating electrolytically galvanized orhot-dip-galvanized steel. After the intended contact time on thesurfaces, the phosphating solutions are not rinsed off with water, butinstead are immediately dried on the lines of a so-called no-rinseprocess. Accordingly, the process according to the invention isparticularly suitable for use in continuous strip treatment plants.

The object of phosphating metals is to produce on the metal surfacefirmly intergrown metal phosphate coatings which improve resistance tocorrosion and, in conjunction with paints and other organic coatings,lead to a significant increase in paint adhesion and in resistance tocreepage in corrosive environments. Phosphating processes have long beenknown. Recently, low-zinc phosphating processes where the phosphatingsolutions have comparatively low contents of zinc ions, for example of0.5 to 2 g/l, have been particularly preferred for pretreatment inpreparation for painting, more particularly electrolytic dip coating asnormally applied in the automotive industry.

In the automotive industry and, in particular, in the domestic applianceindustry, but also for architectural applications, there has been atendency to use galvanized steel strip pre-phosphated in the steel millin order to utilize the more favorable forming properties ofphosphate-coated strip and to save on chemical treatment steps beforepainting. Accordingly, increasing importance is being attached tophosphating processes which lead to high-quality phosphate coatingsdespite the short phosphating times of the strip mill of only a fewseconds. The treatment is normally carried out by spraying, by immersionor by combined spraying/immersion, the phosphating solution being rinsedoff from the metal surface with water after the required contact time.One such process is described, for example, in DE-A-42 41 134, accordingto which phosphating solutions containing 1.0 to 6.0 gl of zinc and 8 to25 g/l of phosphate are used. Other optional components are nickel,cobalt, manganese, magnesium and calcium each in quantities of 0.5 to5.0 g/l, iron(II) in quaintities of up to 2 g/l and copper in quantitiesof 3 to 50 mg/l.

2. Related Art

The hitherto necessary removal of the phosphating solution by rinsingoff with water leads on the one hand to a high consumption of freshwater in the phosphating plant and, on the other hand, results in theaccumulation of wastewater contaminated with heavy metals which has tobe treated for reuse or for discharge into the main drains. The conceptof no-rinse phosphating has already been discussed in the literature (G.Carreras-Candi: "Characteristiques de la Phosphatation sans Rincage" . .. , Surfaces 106 (1976), Number 15, pages 25-28) without any concreteinformation on how the process is carried out or on suitable treatmentbaths.

DE-C-27 39 006 describes a phosphating process which eliminates the needfor rinsing with water which is undesirable from the environmental andcost point of view. In this process, the surfaces are contacted for 1 to5 seconds at 50 to 75° C. with a phosphating solution which contains 0.1to 5 g/l of zinc, 1 to 10 parts by weight of nickel and/or cobalt perpart by weight of zinc, 5 to 50 g/l of phosphate and--asaccelerator--0.5 to 5 g/l of hydrogen peroxide. The surfaces areimmediately dried without rinsing. The use of phosphating solutionscontaining more than 5 g/l of zinc is discouraged because they have anadverse effect on paint adhesion.

EP-B-141 341 also describes a no-rinse phosphating process. This processwas developed in particular for fixed structures, such as bridges or thelike. Accordingly, the surfaces to be protected are treated with asolution containing 1 to 5% by weight of zinc, 1 to 20% by weight ofphosphoric acid, 0.01 to 0.5% by weight of cobalt and/or nickel and 0.02to 1.5% by weight of an accelerator. After application of thephosphating solution, for example by wiping, brushing, spread coating,roll coating or spray coating, the solution is left to act for anunspecified time, the solution either reacting out or only partlyreacting. In both cases, the surfaces can be rinsed after exposure tothe phosphating solution.

In contrast to conventional phosphating processes which are used inpreparation for painting, the phosphating solution described above hashigh zinc and phosphate contents. Phosphating solutions in similarconcentration ranges are also known for the deposition of phosphatecoatings onto metal parts which are to be subjected to cold mechanicalforming, for example by drawing or pressing. The relatively thickphosphate coatings deposited, which may be impregnated with oil toenhance their effect, act as lubricants and reduce friction between tooland workpiece. They are not normally suitable as a pretreatment beforepainting because paint adhesion to the thick phosphate coatings undermechanical stressing is very poor. A corresponding phosphating solutionwhich may be used to form phosphate coatings on steel strip or steelwire, acting as a lubricant before cold drawing or other formingprocesses, is described for example in DE-B-25 52 122. According to thisdocument, the solutions used contain zinc in a quantity of 5 to 100 g/land phosphate in a quantity of 10 to 150 g/l and--asaccelerator--nitrate in a quantity of 10 to 80 g/l. The phosphatingsolution is brought into contact with the surface for 5 to 15 secondsand then rinsed off with water.

The problem addressed by the present invention was to providephosphating processes and phosphating solutions which are intended foruse in continuous strip mills and which eliminate the need to rinse thetreated surfaces with water.

BRIEF DESCRIPTION OF THE INVENTION

In a first embodiment, the present invention relates to a process forphosphating surfaces of steel, zinc, aluminium or their alloys bytreatment with acidic zinc- and phosphate-containing solutions anddrying the solutions without rinsing, characterized in that the surfacesare contacted with a phosphating solution which contains 2 to 25 g/l ofzinc ions and 50 to 300 g/l of phosphate ions and which have a pH valueof 1 to 4.

DETAILED DESCRIPTION OF THE INVENTION

Zinc concentrations of 5 to 25 g/l are preferred insofar as they providefor increased process safety. If corrosion control does not have to meetoverly stringent requirements, as for example in the domestic appliancefield, it is sufficient to use zinc as sole layer-forming cation. Forimproved corrosion control, as required for example in automobilemanufacture, it is preferred to use a phosphating process in which thephosphating solution additionally contains 2 to 25 g/l and preferably 5to 25 g/l of manganese ions. In addition to or instead of the manganeseions, the phosphating solution may contain other components to optimizethe properties of the phosphate coating for the intended application ofthe pretreated material. For example, the phosphating solution mayadditionally contain one or more divalent metal ions in quantities of0.1 to 15 g/l, these additional metal ions preferably being selectedfrom nickel, cobalt, calcium and magnesium. In addition, the phosphatingsolution may contain iron in quantities of 0.01 to 5 g/l and/or 3 to 200mg/l of copper ions. Depending on the substrate, additions of fluoridein free or complexed form, for example as fluoro complexes of boron,silicon, titanium or zirconium, can have a favorable effect on layerformation. This is particularly the case in the phosphating ofhot-dip-galvanized steel. The effective quantities of fluoride arebetween 0.01 and 5 g/l. At pH values above 3, which can be of advantagein the surface treatment of electrolytically galvanized steel, thephosphating solutions tend to become unstable. They can be stabilized byaddition of 0.1 to 100 g/l of a chelating hydroxycarboxylic acidcontaining 3 to 6 carbon atoms. Examples of such hydroxycarboxylic acidsare lactic acid and, in particular, citric acid and tartaric acid.

The free acid content of the phosphating solution is preferably in therange from 0 to 100 points. The free acid point count is determined bytitrating 10 ml of the phosphating solution with 0.1 N sodium hydroxideto a pH value of 3.6. The consumption of sodium hydroxide in mlindicates the free acid point count. If the phosphating solution alreadyhas a pH value of 3.6, the free acid point count is thus 0. Conversely,at higher pH values, the phosphating solution is titrated with 0.1 Nhydrochloric acid to a pH value of 3.6. The free acid point count isthus negative and is equated with the consumption of hydrochloric acidin ml provided with a negative symbol. The total acid content isdetermined by titrating 10 ml of the phosphating solution with 0.1 Nsodium hydroxide to a pH value of 8.5. The consumption of 0.1 N sodiumhydroxide in ml indicates the total acid point count. For thephosphating solution according to the invention, the total acid contentis preferably in the range from 40 to 400 points. The ratio of free acidto total acid is preferably adjusted to lie in the range from 1:4 to1:20.

Phosphating solutions with a temperature of 15 to 80° C. and, moreparticularly, 20 to 40° C. are preferably used. The active substancecontent of the phosphating solutions should be in the range from about5.5 to about 35% by weight. The active substance content is defined asthe sum of metal ions, phosphoric acid and any of the other componentsmentioned.

The process according to the invention is particularly designed forphosphating travelling metal strips in strip treatment plants asencountered, for example, in steel mills. A liquid film coating of 2 to10 ml of phosphating solution per m² of metal surface is preferablyapplied to the surfaces. The optimum value for the liquid film coatingis determined, on the one hand, by the active substance content of thephosphating solution and, on the other hand, by the plant-specificcontact time of the phosphating solution. At the strip speeds of 10 to300 m/minute normally encountered at the present time, weights of thephosphate coatings of around 0.3 to around 3 g/m², as required forsubsequent painting, are obtained with liquid film coatings of around 6ml/m². In general, the concentrations of the phosphating solution shouldbe higher, the smaller the liquid film coating.

Application of the phosphating solution to the surface and adjustment ofthe required liquid film coating can be carried out in various ways. Forexample, the phosphating solution may be sprayed onto the surface insuch a way that the required liquid film coating is established.However, greater process safety is achieved if the liquid film coatingis specifically adjusted after the phosphating solution has been sprayedon, for example by blowing with compressed air or preferably bysqueezing rollers. Instead of being sprayed on, the phosphating solutionmay also be applied to the surface by applicator rolls, in which casethe required liquid film coating can be directly adjusted. Applicatorrolls are known for the surface treatment of metal strips, for exampleunder the name of "chemcoater" or "roll coater". In addition, theprocess may be carried out in such a way that the surfaces dip into thephosphating solution. Metal strips may be passed, for example, throughthe phosphating solution, the required liquid film coating beingadjusted on the surface after the strip has left the phosphatingsolution, for example by blowing with air or preferably by means ofsqueezing rollers.

The optimum process parameters are dependent upon the specific materialproperties of the surfaces to be treated. For example, it has been foundthat, in the treatment of surfaces of travelling strips ofhot-dip-galvanized steel, optimal phosphating results are obtained whenthe phosphating solution has an active substance content of 5.5 to 35%by weight. The preferred pH value is in the range from 1.0 to 2.2 andthe ratio by weight of the sum of the divalent metal ions to phosphateis preferably adjusted to a value of 1:5 to 1:6.

In the treatment of hot-dip-galvanized steel, the presence of free orcomplexed fluoride in the phosphating solution has a favorable effect onlayer formation. Fluoride concentrations of 0.5 to 1.5 g/l areparticularly effective. Free fluoride is preferably used in the form ofhydrofluoric acid while complex fluorides are preferably used in theform of fluoro acids of boron, silicon, titanium and/or zirconium.Alkali metal fluoride or acidic alkali metal fluorides, such as KHF₂,may also be used to make free fluoride available.

By contrast, in the treatment of surfaces of travelling strips ofelectrolytically galvanized steel, the best results are obtained whenthe following conditions are established: an active substance content ofthe phosphating solution of 5.5 to 20% by weight, a pH value of 1.5 to3.5, a ratio by weight of the sum of divalent metal ions to phosphate of1:5 to 1:6. Phosphating solutions with these bath parameters tend tobecome unstable, particularly if the pH value is adjusted in the upperhalf of the range mentioned. The stability of the bath can be improvedby addition of around 1 to 5% by weight of a chelating hydroxycarboxylicacid containing 3 to 6 carbon atoms, for example lactic acid and,preferably, citric acid and/or tartaric acid.

In the treatment of surfaces of travelling strips of cold-rolled,ungalvanized steel, the following conditions are preferably established:an active substance content of the phosphating solution of 5.5 to 25% byweight, a pH value of 2.0 to 4.0, a ratio by weight of the sum of thedivalent metal ions to phosphate of 1:5 to 1:6. In this case, too, bathstability can be improved by addition of around 1 to 10% by weight of achelating hydroxycarboxylic acid containing 3 to 6 carbon atoms, forexample lactic acid and, preferably, citric acid and/or tartaric acid.

There is no need to use so-called accelerators, i.e. substances whichpromote layer formation by virtue of their oxidizing or reducing effect,particularly in the treatment of galvanized steel. However, it canafford advantages where the development of certain crystal forms isrequired. Suitable accelerators are any of the compounds known from therelevant prior art, more particularly nitrate, nitrite, chlorate,nitrobenzene sulfonic acid or hydrogen peroxide. Hydroxylamine may beused as an accelerator with more of a reducing effect. Hydrogen peroxideand hydroxylamine may be used as such whereas the other acceleratorsmentioned may be used as free acids or in the form of salts soluble inthe phosphating solution. However, since only a small quantity ofwater-soluble salts, if any, should remain behind on the surface afterthe phosphating solution has dried, it is advisable to avoid alkalimetal and ammonium salts and also sulfates. Accelerators which do notleave salt-like residues behind on the treated surfaces are particularlypreferred. Accordingly, hydroxylamine and, in particular, hydrogenperoxide are particularly suitable. Where accelerators are used, theirpreferred concentrations are from 2 to 5 g/l for hydroxylamine,nitrobenzene sulfonic acid and chlorate, from 0.2 to 1 g/l for nitriteand from 20 to 100 ppm for H₂ O₂.

According to the invention, the liquid film remaining on the surfaceafter application of the phosphating solution is not rinsed off, butinstead is dried. To this end, the surfaces are preferably heated to atemperature of 50 to 120° C. and more preferably to a temperature of 60to 90° C. Various possibilities are available in this regard. Forexample, the treated steel strip may be passed through a drying ovenheated to the corresponding temperature. However, drying may also becarried out by blowing hot gases, preferably air, onto the surfacesand/or by exposing the surfaces to infrared radiation. Since the acidicphosphating solution can react chemically with the metal surface as longas it is still liquid, the effective contact time is defined as the timeelapsing between the first contact of the surface with the phosphatingsolution and the complete drying of the liquid film on the surface, i.e.the end of the drying step. This time is preferably between about 3 andabout 60 seconds.

Under the process conditions mentioned, phosphate coatings with a weightof 0.3 to 3 g/m² are produced on the surfaces. Coating weights of thisorder are particularly desirable as a basis for subsequent paintingbecause the two requirements of corrosion control and paint adhesion areboth satisfied to a particular degree in this way. Depending on how theprocess is carried out, coatings are obtained which do not yield anyreflexes in X-ray diffraction studies, i.e. may be regarded as X-rayamorphous, or which show more or less pronounced reflexes of hopeite.

The strips prephosphated by the process according to the invention maybe used in particular in the manufacture of automobiles. It is standardpractice in this regard to rephosphate and then paint the bodies(normally by cathodic electrodeposition coating) after assembly. Inthese cases, the material prephosphated by the process according to theinvention is transported in the unpainted state to the furtherprocessor. To improve temporary corrosion control during storage andtransportation, the phosphated material may be additionally oiled.Subsequent forming operations are also made easier in this way.Rephosphating of the assembled bodies after alkaline cleaning is readilypossible.

However, phosphating in accordance with the invention may also beimmediately followed by coating of the strip with an organic film or alacquer. This process is known as coil coating. Coil-coated material isat present mainly used in the manufacture of domestic appliances suchas, for example, refrigerators and washing machines and also forarchitectural applications.

In the prior art, it is standard practice for phosphating to be precededby so-called activation. The object of activation is to allow crystalnuclei for the formation of the phosphate coating to form on the metalsurface. The formation of dense, small-crystal phosphate coatings ispromoted in this way. At present, aqueous solutions or suspensions oftitanium phosphates are exclusively used for activation. The processaccording to the invention may also be preceded by an activatingtreatment. The activating treatment may be carried out with commerciallyavailable titanium phosphate activators such as, for example, Fixodine®950, a product of Henkel KGaA. Where the process according to theinvention is preceded by an activating treatment, it is advisable to drythe strip between activation and phosphating.

In another embodiment, the present invention relates to a zinc- andmanganese-containing aqueous acidic phosphating solution for phosphatingsurfaces of steel, zinc, aluminium or their alloys, characterized inthat it contains 2 to 25 g/l of zinc ions, 2 to 25 g/l of manganese ionsand 50 to 300 g/l of phosphate ions and has a pH value of 1 to 4.

In addition, the phosphating solution may contain one or more of theother components mentioned above in the description of the process.Similarly, the conditions mentioned above also apply to the preferredcontents of Zn, Mn and any other metal ions, to the free acid and totalacid contents and to the preferred ratio of free acid to total acid.

EXAMPLES

Steel plates of the ST 1405 quality, steel plates electrolyticallygalvanized on both sides (ZE) with a zinc coating of 7.5μ and steelplates hot-dip-galvanized on both sides (Z) with a zinc coating ofaround 10μ were used for the laboratory testing of the phosphatingprocess according to the invention. The plates all had dimensions of 10cm by 20 cm. Before phosphating, they were degreased with a commerciallyavailable mildly alkaline cleaner (Ridoline® 1250 I, a product of HenkelKGaA, Dusseldorf). The no-rinse treatment was simulated by pouring thetreatment solution into a paint thrower (Model 4302 of Lau GmbH) andapplying it at 550 r.p.m. A wet film coating of about 6 ml/m² was formedin this way. After the treatment solution had been applied for about 5seconds, the plates were immediately dried for about 120 seconds in arecirculating air drying cabinet heated to 75° C.

The coating weight was determined as the parameter for the phosphatecoating obtained. Two different methods were used for this purpose. Todetermine the weight of the coating by weighing out, the plate wasweighed before coating, the phosphating solution was applied and driedand the coated plate was reweighed. The coating weight in g/m² wascalculated from the weight difference. To determine the weight of thecoating by dissolution, the phosphated plates were weighed, thephosphate coating was removed by dissolving with 0.5% by weight chromicacid solution and the plates were reweighed. The weight of the coatingremoved in g/m² was determined from the weight difference. The coatingweight determined by dissolution is generally higher than thatdetermined by weighing out because the phosphating process converts partof the metal surface into metal phosphate. This part is not included indetermination of the coating weight by weighing out, but is removed withthe coating where coating weight is determined by dissolution.

Table 1 contains phosphating baths for electrolytically galvanized steeland the coating weights obtained while Table 2 contains correspondingExamples for the treatment of hot-dip-galvanized steel. Phosphatingsolutions which lead to coating weights of 1 to 3 g/m² are suitable forthe treatment of these substrates. In the treatment baths of theExamples, zinc was used as oxide, manganese and nickel as carbonate andfluoride as sodium fluoride. Apart from water, the baths contained noother components.

For Example 20, the composition of the coating was determined in % byweight by EDX (X-ray emission): Zn 7.5, Mn 2.2, P 7.5, Al 0.3,remainder: may be recorded as oxygen.

A selection of Z plates treated in accordance with the invention wassubjected, as in practice, to conventional automotive rephosphating by acommercial trication phosphating process (Granodine® 1994, a product ofHenkel KGaA, Dusseldorf) and painted with a cathodic electrocoatingpaint (Aqualux® K, a product of IDAC). After a corrosion test (10 cyclesof alternating climate according to VDA 621 415), the creepage of rustbeneath the lacquer at a cut was measured in accordance with DIN 53167.The following results were obtained:

    ______________________________________                                                Example l9                                                                           1.9 mm                                                                Example 20                                                                                 2.2 mm                                                           Example 22                                                                                 2.4 mm                                                           Example 24                                                                                 2.3 mm                                                    ______________________________________                                    

                  TABLE l                                                         ______________________________________                                        No-rinse Phosphating of Electrolytically Galvanized Steel                                       Active                                                                        Sub-                                                                          stance      Free   Total                                                                                 Coating                          Ex.  Bath Composition                                                                           [% by          Acid                                                                              Acid     Weight.sup.1)                   No.  [g/l ]       weight]  pH [points]                                                                            [points]                                                                            [g/m.sup.2 ]                        ______________________________________                                         1   210    H.sub.3 PO.sub.4 85%                                                           Zn5            21.4                                                                              1.5                                                                             65     303                                                                                 1.57 (W)                                    Mn20                                                              2     105   H.sub.3 PO.sub.4 85%                                                         Zn7.5                 2.5                   0.40 (W)                          Mn0.0                                                              3     210  H.sub.3 PO.sub.4 85%                                                           Zn5            21.4                                                                                314    281                                                                                 1.75 (W)                                    Mn0                                                               4    140     H.sub.3 PO.sub.4 85%                                                        Zn10.0                2.5                  0.90 (W)                           Mn3.3                                                                                                            1.62 (D)                        5    175   H.sub.3 PO.sub.4  85%                                                         Zn2.5                 29      228                                                                                1.34 (W)                                   Mn16.6                                                                                                                 1.96 (D)                  6    140   H.sub.3 PO.sub.4 85%                                                          Zn0.0                 2.2                  0.76 (W)                           Mn13.3                                                                                                               1.47 (D)                    7    140   H.sub.3 PO.sub.4 85%                                                          Zn0.0                  2.1                 0.81 (W)                           Mn13.3                                                                                                               1.35 (D)                    8    110   H.sub.3 PO.sub.4 85%                                                          Zn.5                 272.5                                                                                190    1.24 (D)                                   Mn10.0                                                                        2.5                                                                           Ni                                                                 9    110   H.sub.3 PO.sub.4 85%                                                         7.5                                                                            Zn                                                                            10.0                                                                          Mn                     3.0                 1.73 (D)                           Ni2.5                                                                         tartaric acid                                                     10      110  H.sub.3 PO.sub.4 85%                                                         Zn7.5                                                                         10.0                                                                          Mn                      3.5              2.05 (D)                             2.5                                                                           Ni                                                                          20.0                                                                            tartaric acid                                                     11   100    H.sub.3 PO.sub.4 85%                                                          Zn6                                                                           Mn              11.0                                                                                 3.0                                                    1                                                                             fluoride                                                                    10                                                                              tartaric acid                                                     12   110    H.sub.3 PO.sub.4 85%                                                          Zn6             11.4                                                                                 3.2               1.44 (D)                             Mn                                                                            tartaric acid                                                     13    210   H.sub.3 PO.sub.4 85%                                                          Zn 15           21.4                                                                                 .2                1.8 (D)                              Mn20                                                              14*.sup.)                                                                          210    H.sub.3 PO.sub.4 85%                                                          Zn  15          21.4                                                                                2.2              1.8 (D)                                Mn 20                                                             ______________________________________                                         .sup.1) W: determined by weighing out D: determined by dissolution            .sup.*) In Example 14, the plate was activated for 5 seconds before           phosphating by immersion in an activating bath based on titanium phosphat     (Fixodine ® 950, Henkel KGaA, 0.3% in deionized water) and dried for      minutes at 75° C.                                                 

                  TABLE 2                                                         ______________________________________                                        No-rinse Phosphating of Hot-dip-galvanized Steel                                                Active                                                                        Sub-                                                                          stance      Free   Total                                                                                 Coating                          Ex.  Bath Composition                                                                           [% by          Acid                                                                              Acid     Weight.sup.1)                   No.  [g/l]        weight]  pH [points]                                                                            [points]                                                                            [g/m.sup.2 ]                        ______________________________________                                        15   280    H.sub.3 PO.sub.4 85%                                                          Zn        20                                                                                  27.8                                                                                813    365                                                                                0.73 (W)                                    Mn       20                                                       16     560  H.sub.3 PO.sub.4 85%                                                          Zn       40                                                                                   55.6                                                                                0.6                     7.15 (W)                        Mn        40                                                      17     328  H.sub.3 PO.sub.4 85%                                                          Zn      24.0                                                                                        1.1                 2.72 (W)                            Mn       23.4                                                     18    305   H.sub.3 PO.sub.4 85%                                                          Zn      22.0                                                                                        1.2                   2.57 (W)                          Mn       21.1                                                     19     210  H.sub.3 PO.sub.4 85%                                                          Zn      15.3                                                                                       734     294                                                                                1.50 (W)                                    Mn       15.0                                                     20    210   H.sub.3 PO.sub.4 85%                                                          Zn       15                                                                                   22.0                                                                               65.5    303                                                                                1.8 (W)                              20     Mn                                                                21    301   H.sub.3 PO.sub.4 85%                                                          Zn       15                                                                                   28.7                                                                                 1.0                2.63 (W)                            Mn      15                                                                    fluoride                                                          22    221   H.sub.3 PO.sub.4 85%                                                          Zn15                 671.5                                                                               321     1.55 (W)                                   Mn 15                                                                         Ni   5                                                            23    268   H.sub.3 PO.sub.4 85%                                                          Zn  12          25.2                                                                                1.0                2.10 (W)                             Mn   12                                                                       fluoride8                                                         24     241  H.sub.3 PO.sub.4 85%                                                          Zn  10.8              1.1            1.46 (W)                                 Mn   10.8                                                                     fluoride.7                                                        25    240   H.sub.3 PO.sub.4 85%                                                          Zn   20                 1.1            1.58 (W)                               fluoride                                                          ______________________________________                                         .sup. 1) See Table 1                                                     

                  TABLE 3                                                         ______________________________________                                        No-rinse Phosphating of Cold-rolled Steel (ST1405)                                                Active           Coating                                  Ex.   Bath composition                                                                             Substance             Weight.sup.1)                      No.   [g/l ]         [% by weight]                                                                            pH   [g/m.sup.2 ]                             ______________________________________                                        26    80     H.sub.3 PO.sub.4 85%                                                                     12.4      3.0  1.4 (D)                                             Zn 8                                                                          Mn 8                                                                          citric acid                                                      27     74    H.sub.3 PO.sub.4 85%                                                                           13          2.1 (D)                                          Zn 7.4                                                                        Mn7.4                                                                         citric acid                                                      28    65     H.sub.3 PO.sub.4 85%                                                                           17.5                                                                                      1.5 (W)                                        10                                                                              Zn                                                                            5                                                                             Mn                                                                            Fe(II)                                                                        citric acid                                                      29     100   H.sub.3 PO.sub.4 85%                                                                          15.8        2.3 (D)                                          10                                                                             Zn                                                                            10                                                                            Mn                                                                            citric acid                                                                   hydroxylamine                                                    30      70   H.sub.3 PO.sub.4 85%                                                                         10.5         1.8 (D)                                           Zn                                                                            Mn7                                                                           citric acid                                                                   hydroxylamine                                                    ______________________________________                                         .sup.1) See Table 1                                                      

We claim:
 1. In a process for phosphating a surface of steel, zinc,aluminium or their alloys by treatment with an acidic, zinc- andphosphate-containing solution and drying the surface without rinsing,the improvement which comprises: contacting the surface with aphosphating solution containing 2 to 25 g/l of zinc ions, 2 to 25 g/l ofmanganese ions and 50 to 300 g/l of phosphate ions and having a pH valueof 1 to 3.6, a free acid content of 0 to 100 points, a total acidcontent of 40 to 400 points and a ratio of free acid to total acid notgreater than 1:4.
 2. The process as claimed in claim 1, wherein thephosphating solution additionally contains at least one of the followingcomponents:(a) at least one divalent metal ion selected from the groupconsisting ofNi, Co, Ca, Mg in a quantity of 0.1 to 15 g/l, copper in aquantity of 3 to 200 mg/l, iron in a quantity of 0.01 to 5 g/l; (b) 0.01to 5 g/l of fluoride in free or complexed form; and (c) 0.1 to 100 g/lof a chelating hydroxycarboxylic acid containing 3 to 6 carbon atoms. 3.The process as claimed in claim 1 wherein the phosphating solution is ata temperature of 15° C. to 80° C.
 4. The process as claimed in claim 1wherein the phosphating solution has an active substance content of from5.5% to 35% by weight of the solution.
 5. The process as claimed inclaim 1 wherein the solution is applied to the surface of a moving metalstrip.
 6. The process as claimed in claim 1 wherein the phosphatingsolution is sprayed onto the surface to be phosphated at a liquid filmcoating of 2 to 10 ml/m².
 7. The process as claimed in claim 1 whereinthe phosphating solution is applied to the surface to be phosphated byapplicator rolls at a liquid film coating of 2 to 10 ml/m².
 8. Theprocess as claimed in claim 1 wherein the surface to be phosphated isimmersed in the phosphating solution and, after leaving the phosphatingsolution, a liquid film coating of 2 to 10 ml/m² is formed on thesurface.
 9. The process as claimed in claim 1 for treating the surfaceof a strip of hot-dip-galvanized steel, wherein the phosphating solutionhasan active substance content of 5.5% to 35% by weight; and at leastone ofa pH value of 1.0 to 2.2; and a ratio by weight of a sum ofdivalent metal ions to phosphate of 1:5 to 1:6.
 10. The process asclaimed in claim 1 for treating the surface of a moving strip ofelectrolytically galvanized steel, wherein the phosphating solutionhasan active substance content of from 5.5% to 20% by weight of thesolution, and at least one ofa pH value of 1.5 to 3.5 and a ratio byweight of a sum of divalent metal ions to phosphate of 1:5 to 1:6. 11.The process as claimed in claim 1 for treating a surface of cold-rolledungalvanized steel, wherein the phosphating solution has an activesubstance content of from 5.5% to 25% by weight of the solution, and thesolution has at least one ofa pH value of 2.0 to 3.6 and a ratio byweight of a sum of divalent metal ions to phosphate of 1:2.5 to 1:6. 12.The process as claimed in claim 1 wherein the drying is carried out at atemperature of 50° C. to 120° C., and the time elapsing between thefirst contact of the surface with the phosphating solution and the endof the drying step is from 3 to 60 seconds.
 13. The process as claimedin claim 1 wherein a crystalline or X-ray-amorphous, zinc-containing,phosphate coating with a coating weight of 0.3 to 3 g/m² is formed. 14.The process as claimed in claim 2 wherein the phosphating solution is ata temperature of 15° C. to 80° C.
 15. The process as claimed in claim 2wherein a percent of active substances in the phosphating solution isfrom 5.5% to 35% by weight.
 16. The process as claimed in claim 3wherein a percent of active substances in the phosphating solution isfrom 5.5% to 35% by weight.
 17. The process as claimed in claim 14wherein a percent of active substances in the phosphating solution isfrom 5.5% to 35% by weight.
 18. The process as claimed in claim 1wherein the ratio of free acid to total acid is from 1:4 to 1:20. 19.The process as claimed in claim 2 wherein the ratio of free acid tototal acid is from 1:4 to 1:20.